Preparation of aromatic polycarboxylic acids



.ofa metal and bromine.

PREPARATION OF AROMATIC POLYCAR- BOXYLIC ACIDS -All-red Satfer, Bayside,N. Y., and. Robert-Sr Barker,

Plainfield, N. J., assignors, by mesne assignments, to Mid-CenturyCorporation, Chicago, 111., a corporation of Delaware .No. Drawing.Application August 24, 1955 Serial No. 530,401

12 Claims. ((11. 260-524) The invention relates. to-a process for thecatalytic oxidation of organic compounds. More particularly, .itpertains to the oxidation of aromatic compounds. con- .taining one ormore aliphatic substituents .to produce corresponding aromaticcarboxylic acids using. molecular oxygen as the oxidizing means, andespecially toa liquid phase oxidation process catalyzed by the conjointpresence Further, the invention includes correlated improvements anddiscoveries-whereby the oxidation, particularly of aromatic compoundscontaining an aliphatic substituent, is facilitated.

Numerous aromatic carboxylic acids may be prepared by catalyticoxidation of alkyl substitutedaryl compounds by means of gaseous oxygenaccording to this invention, some of these acids, such as thephthalicacids, being'now available in commerce. However, 'such'acids*may" be produced according to thBfPlBSEDt inventiomwith 'increasedeconomy and convenience from-readily available rawmaterials. Moreover,practice of'the present invention enables economical production ofnumerous aromatic and alkaryl acids which havepreviouslylbeenunavailable except at inordinate cost. A'particularlyadvantageous field of application of the present inventionjs inproduction of polycarboxylic aromatic acids.

organic compounds containing atleast one and preferably apluralityofaliphatic sub'stituents in 'the conjoiht 'presence of a metaland bromine to produce carboxy aromatic compounds; aprocess. forcatalytic ox dation-in .liquid phase by' means of molecular oxygen, tocarboxy aromatic compounds, of an aromatic compound having at leastoneand preferably .a pluralityof aliphaticsubstituents wherein thealiphatic carbon atom attached .directly to an aromatic nucleus in atleast one of such aliphatic substituents'contains at least onehydrogen'or oxygen atom, in the conjoint presence of metal or metal ions andbromine or bromine ions; such processes wherein the metal is a heavymetal; such processes wherein at least-one aliphatic substituentcontains from 1 to 4 carbon atoms per aromatic nuclear carbon atom towhich it is attached; such processes carried out in the presence of anacid, such .as for example, a lower aliphatic mono carboxylic acidcontaining 1 to .8 carbon atoms in the molecule, said acid being inliquid phase, and preferably being saturated:- and containing.24 carbonatoms in the molecule -andpreferably employing about 0.1- parts byweight .of such acid per part by weight of aliphatic substituted"aromatic compound; such, processes whereinthe catalyst is manganesebromide or cobalt bromide .or combinations thereof; such processes.wherein'the catalyst 'is provided as a mixture of a lower aliphaticcarboxylate' salt of 'the'desired metal and a bromide .or bromate;:'suchprocesses applied specifically to alkyl benzeneswher'ein each alkylsubstituent contains 1 to 4 carbon"atoms;"and

other such processes and modifications thereof aswill'be as-.'-theborates, halides and nitrates which are also em- 2,833 ,816 PatentedMay. 6, 1 958 ..apparent as details or embodiments of the invention areset forth hereinafter.

In the practice of the invention, the oxidation of organic compoundswhereby corresponding aromatic carboxylic acids, particularlypolycarboxylic acids, are obtained, may

.be effected by reacting such compounds with molecular oxygen, e. g.air, in the conjoint presence of catalytic amounts of a metal and ofbromine. Metals of the .group of heavy metals shown in the Periodic.Chart of Elements appearing on pages 56and 57 of the Handbook ofChemistry, 8th edition, published by. Handbook' Publishers, Inc.,Sandusky, Ohio,'1952,' have been found desirably applicable to thisinvention for furnishing the metal or metal ion portion ofthemetal-bromine .catalyst. anatomic number not greater than .84 havevbeen found most suitable.

Of the heavy metal group, those metals having However, as will appear,metals .outside the heavy metal group may also be employed. We have alsofound that excellent results are obtained by theutili- .zation of ametal having an atomic number'23-i28, inclusive. .Particularly excellentresults are obtained .with

a metal of the group consisting. of manganese, cobalt, nickel, chromium,vanadium, molybdenum, tungsten, tin .and cerium. It has also been foundthat the catalytic amount of the metal may be either as a single metalor as-a combination of such metals.

lhavebeen obtained, forexample, withpotassiurn brovmate,tetrabromoethane and benzyl bromide.

. The metal may be supplied in the form of metal. salts.

. For example, the metal manganese. may be supplied as the manganesesalt of a lower aliphatic carboxylic' acid, such as manganese acetate,in the form of'an organic complex, of which mention may be made of ,the'acetylacetonate, the S-hydroxy-quinolinate andthe ethylene diaminetetra-acetate, as well as manganese 'salts'; such ca'cious.

.'The reaction temperature should be sufiicientlyhigh so 'thatthede'sired oxidation reaction occurs,'and'. yet

.not sohigh as to cause undesirable charring orformation fof tars. Thus,temperatures in the range of to 275 "C., desirably to 250 C., andpreferably 10225 C. may be employed. The reaction time should be*sufiicient to obtain a desirable conversion of the substituted.aromatic material to the desired aromatic carboxy compound, e. g., inthe range of about 015 to 25.,or more ..hours, preferably up to about 4hours.

The oxygen used may be in the fOI'Il'l'Of substantially 100% oxygen gasor in the formof. gaseouspmixtures containing lower concentrationsofoxygen, such..as, .for :example, air. The ratio of total oxygemfedintothe reaction mixture relative to the hydrocarbonis in the ,range ofabout 2 to 500 mols of oxygenper mol of =subthe feed is notsubstantially vaporized. "The relation of temperature and pressureshould: be so -regulated as to provide a liquid phase in the reactionzone. Generally, the pressure may be in the range of atmospheric up to-about 1500 p; s. i. g. The liquid phase may compriseall or a p'ortionofthe organic reactant or itrnay comprise a reaction medium in which theorganic reactant'is-soluble or suspended.

iii

When the conditions are such that the desired carboxy aromatic productmay be obtained and readily separated from the reaction mixture in theabsence of additional reaction medium, such added medium is notrequired. However, where all such conditions do not obtain or where thepresence of an added reaction medium is desired to facilitate carryingout the desired reaction or recovering the desired product or products,an added medium may be included. This added medium may be, and oftendesirably is, a monocarboxylic acid relatively stable or inert tooxidation in the reaction system, preferably containing about 1 to 8carbon atoms in the molecule. Saturated aliphatic acids containing 2 to4 carbon atoms in the molecule and free of hydrogen atoms attached totertiary carbon atoms are particularly preferred. Where all theadvantages of an acid medium are not required, other inert media can beused.

Where the lower aliphatic monocarboxylic acid medium is used, it isgenerally not necessary to use large amounts thereof. Such acids in therange of 0.1 to parts by weight, desirably 0.5 to 4, and preferably 1 to2.5 per part of the aromatic material, have been found adequate.

The catalyst, illustratively, may be manganese bromide, and it may beadded as such or by means of materials which provide a catalytic amountof manganese and of bromine in the reaction system. Manganese may beadded in the form of the metal, oxide or acetate or analogouscarboxylate salts including a salt of a carboxylic acid which may beformed in the reaction system or as a manganese halide; and the brominemay, as above indicated, be added in the form of elemental bromine, asammonium bromide or other bromine compounds soluble in the system, e. g.potassium bromate. If desired, the bromine may be in the form of asoluble organic bromide, viz. tetrabromoethene, benzyl bromide, and thelike. The amount of the catalyst calculated as MnBr may be in the rangeof about 0.1 to 10 percent by weight or more of the aromatic reactantcharged, desirably 0.3 to 2, and preferably 0.5 to 1.7 percent. Mixturesof materials may be used; and the proportions of manganese and brominemay be varied from their stoichiometric proportions encountered in MnBre. g., in the range of about 1 to 7 atoms of manganese per atom ofbromine, and about 1 to 10 atoms of bromine per atom of manganese.Moreover, the manganese may, as above indicated, be utilized in the formof an organic complex by way of example as the acetylacetonate, theS-hydroxy quinolinate, and the ethylene diamine tetra acetate ofmanganese.

In order to facilitate a clear understanding of the invention, thefollowing preferred specific embodiments are described in detail:

Example 1 Into a suitable reactor having a corrosion resistant innersurface (e. g. glass, ceramic or corrosion resistant metal or alloy),equipped with agitating means such as a mechanical agitating device orgas flow agitating means,

and with means for heating or cooling the contents thereof such as acoil or jacket (and optionally a reflux condenser equipped with aseparatory device for separating water and refluxing non-aqueouscondensate to the reaction vessel, 21 gas inlet tube, and a vent forpassing off low boiling materials), there are charged:

48.8 parts by weight of xylene (95 para) 125 parts of acetic acid(100%).

0.6 part of manganese acetate 0.5 part of ammonium bromide The reactionvessel is about half filled with the liquid mixture.

Air is fed into the reaction mixture at the rate of 3000volumes/hour/volume of reaction mixture (measured at is maintained atabout 200 to 400 p. s. i. g. (pounds per square inch gauge); thispressure being such that the re action mixture contains a liquid phasecontaining acetic acid.

The crude solid terephthalic acid in the mixture may be separated byfiltration, given three washings with about acetic acid, each washingbeing withabout 100 parts by weight of acetic acid per 40 parts of theprecipitate, and then given three washings with water, usingapproximately similar amouuts. The acetic acid washings are distilled;the residue may be recycled to the reactor or may be processed torecover a mixture of aromatic acids therefrom. The exit gases from thereactor. are passed through two Dry Ice traps in series, and the liquidcollected therein during the reaction wa washed with about 2 volumes ofwater to remove water soluble Inaterials therefrom, and a small amountof unreacted xylene is recovered.

A light colored terephthalic acid product is obtained in a weight yieldof about 118 percent (75 of theory). Similar results are obtained withmanganese or cobalt bromide as the catalyst. However, with manganesechloride alone, only about 25-30% by weight yield was obtained (afour-fold to five-fold cliflcrence) under comparable conditions. Theresults obtained with manganese fluoride, acetate or iodide, or ammoniumbromide (i. e. hydrogen bromide in the acidic system) without a metal,are less favorable than with the manganese chloride.

Example 2 The above example is repeated except using:

parts para-cymene 125 parts acetic acid 1.2 parts manganese acetate 0.95part ammonium bromide and a terephthalic acid yield of 58.6% of theoryis obtained which corresponds to a 73% weight yield. With manganesesbromide similar results (73% by weight yield) are obtained. However, ina comparable run using solely two parts manganese acetate as thecatalyst, the yield was not over about 7% by weight (a ten-folddifference); and using manganese chloride, it was even lower.

Example 3 The above Example 2 is repeated except using a diethylbenzenemixture, and about 58% by weight yield of phthalic acids are obtained.

The above examples are repeated and comparable yields of thecorresponding phthalic acids are obtained from the following startinghydrocarbons:

Example N0. Hydrocarbon Acid Obtained p-n-propyl toluene terephthalic.p-n-butyl toluene Do. p-i-butyl toluene D0. meta-xylene. isophthalic.metacymeneun Do. metu-diethylbenzene Do. meta-n-propyl toluene Do.meta-n-butyl toluene Do. meta-i-butyl toluene Do. ortho-xylene phthalic.ortho-cymene Do. ortho-diethylbenzcne.-. D0. ortho-n-propyl toluene Do.ortho-n-butyl toluene- Do. ortho-Lbutyl toluene Do.

In runs comparable to Examples 7 and 13, except using solely manganesechloride as the catalyst, comparably lower yields of the respective acidare obtained in each instance. A mixture of ethyl toluenes treatedsimilarly with manganese bromide catalyst gives about 75% by weight ofthe mixed phthalic acids.

In the case of the isophthalic acids, the crude solid isophthalic acidin the mixture is separatcd by filtration, and

assent washed with about parts by'weight of benzene. Alternatively, maybe: given three'washings With:about-100% lower carboxylic acid; e. g.,-acetic'acid,. each washing being with about 100 parts by weight of theacid per 40 parts of the precipitate, and then given three washings withwater, using approximately similar amounts. The acetic acid washings arerecycled in. the next run.

In the case of the phthalic acid, the acid may be recovered by heatingto convert to the anhydride .whichmay be sublimed or distilled: andcondensed.

The crude phthalic acids may be converted to the corresponding dialkylphthalates by reaction with methanol or an analogous lower alkanol' of lto 3 carbon atoms in the molecule, in the presence of a catalytic amountof an acid such as hydrochloric, sulfuric, phosphoric or the like, e.g., in an amount in therange-of up to about 3% by weight of thereaction: mixture. Alternatively, they may be first converted to thecorrespondingacid chloride and the latter reacted withmethanol. Theresulting alkyl phthalates may be separated by fractionation, orpurified by steam distillation. They'are useful in the form of theesters, e. g., for preparation of polyester type resins byreaction withpolyhydric materials such as ethylene glycol, or glycerol or the like.If desired, the dialkyl ester may be converted to the acid by hydrolysisin the presence of dilute aqueous acid.

Example 19 The above Example 1 procedure is repeated using:

75 parts mesitylene (1,3,5-trimethylbenzene) 150 parts acetic acid 1part manganese bromide at a reaction temperature of 196 C. and apressure of 400 p. s. i. g., for three hours. The reaction mixture isfiltered at about 50 to 60 C. Methyl'isophthalic acid is obtained in ayield of about weight percent (acid number 627, theory 623).

Example 20 The above Example 19 procedure is repeatedusing: 75 partsmesitylene 175 parts acetic acid 1.5 parts cobalt naphthenate 0.8 parthydrobromic acid (as aqueous solution) at-a temperature of 204 to 210 C.Trimesic acid is ohtained in an. about 83 percent yield (acid number789, theory 800).

Example 21 The above Example 19 procedure is repeated using:

75 parts mesitylene 150 parts acetic acid 1 part manganese bromide 0.5part manganese acetate 0.5 part cobalt naphthenate 0.5 part ammoniumbromide Example 22 I i The above'Example 19 procedure is repeated using?75 parts pseudocumene (1,2,4-trimethylbenzene) 15 0 parts acetic acid1.5 parts cobalt napthenate 1.5 parts manganese acetate.

1.5 parts-ammonium bromide at 198 C; for. two hours. On filtering thereaction mixture, trimellitic acid (1, 2, 4-b enze'ne.tricarboxylicacid) is obtained in an about 92"weight'percent yield.

. 6 Exampl-e23 The above Example 19' procedure is repeated'usingif.

75 parts of ditolylethane 150 parts of acetic acid 1 part manganesebromide at a. temperature of 195 C. for two hours. The reaction mixtureis filtered at about 50 C. and the solid washed with'two 75 part byweight portionsof hot acetic acid (about. 75 C.) and the solid dried toconstant weight. A benzene dicarboxylic acid mixture is obtained in anabout weight percent yield (acid number 680, theory 675). Thismixtureanalyzes as 84% by weight isophthalic and 16% .terephthalic acid: (byaccepted infra-red analysis methods; Analytical Chemistry, November1954, page 1765, January 1955, page 7, and Perkin-Elmer News, .vol- 4,No. 3, .1953) 1 Preparation of diiolylethane.-The following mixture ischarged to a reactor having a'gla'ss inner surface, equipped witha'mechani'cal stirrer, thermometer, reflux condenser, mercury manometer,and two Water bubblers in series:

936 parts of toluene parts of ethylene dichloride 20.2 parts ofanhydrous aluminum chloride The distillation data show-that thealkylation'product contains:

Parts Weight, percent Total 957 The weight yields of alkylation productsbased 'on'the weight of toluene consumed are-77.4% of ditolylethane and25.2% higher polytolylethane.

Example 24 A process is conducted in an apparatus havingin combination acorrosion-resistant pressure oxidation reactor and a water-cooledcondenser mounted above the reactor. The reactor section is Wound withNichrome ribbon to a height of about /a the reactor height. When theoxidation is in progress,-air under pressure is admitted to the reactorthrough a gas distributor located just above the bottom, and the upperend of the condenser is sealed. Vent gases exit through a tube at thetop of the condenser and pass through a needle control valve; 'amercury-inglass flow meter and a Dry Ice trap prior to ventingto theatmosphere. The reactor is charged by adding Weighed amounts of eachreactant through the top ofthecondenser, which is then closed and thereactor pressure raised to about 400 p. s. i. g. with air. Thus thereactor is charged with 75 parts of 95% p-xylene, 150 parts of aceticacid, one part of manganese acetate tetra'hydrate and 0.75 part ofammonium bromide. The pressure isrset at 400 p. s. i. g. and the reactorsection heated to 385 d F. The exit control valve is adjusted sothat theflow rate of gas through the exit flowmeter is 3000 volumes/hour/ volumeof reaction mixture. When the temperature reaches 385 F., the externalheating is, halted and the temperature rises because of the'exothermicity of the reaction'; Afterthe initial reaction, externalheat is applied to maintain a reaction temperature of 385- 400- Fi ter atotal of 1.5 hours. Upon completion of the reaction, as shown by 20-21%oxygen content (Orsat gas analysis) of the exit gas, the reactor isallowed to cool to 185 F. and depressured. The liquid products areremoved at l50-200 F. by applying back pressure from a nitrogen cylinderthrough the condenser. The reactor liquid is drained by opening a unionin the air feed line. The bottom flange is removed and the solid productscraped from the reactor section. The solid and liquid products arecombined and filtered. The insoluble terephthalic acid residue is washedtwice with 75 mls. of hot acetic acid and dried. A weight yield of 115%terephthalic acid is obtained (acid number 672, theory 675).

In comparative runs with paraxylene and a given amount of metal bromide,using a mixture of manganese and cobalt bromides in equal parts, theyield of terephthalic acid is about 12 or more weight percent pointshigher than when using either metal bromide alone.

Example 25 Powdered manganese metal (300 mesh), one part, is substitutedfor manganese acetate in Example 24. The yield of terephthalic acid is110 weight percent.

Example 26 Nickel (II) bromide, one part, is substituted for both themanganese acetate and ammonium bromide in Example 24. A 95 weightpercent yield of terephthalic acid is obtained.

Example 27 Cobalt acetate, one part, is substituted for manganeseacetate in Example 24. A 122 weight percent yield of terephthalic acidis obtained.

Example 28 Example 29 Tungstic acid, one part, is substituted for thecerium hydroxide in Example 28 and a yield of 116 weight percent ofterephthalic acid is obtained.

Example 30 Ammonium molybdate, one part, is substituted for the ceriumhydroxide in Example 28 to yield 114 weight percent of terephthalicacid.

Example 31 A mixture of ammonium meta-vanadate, one part, and chromicacetate, one part, is substituted for cerium hydroxide in Example 28 toyield 108 weight percent of terephthalic acid.

Example 32 One part of Raney nickel alloy which consists of aluminum andnickel is treated with ammonium bromide and HBr as described in Example28 and the resultant catalyst mass is substituted for manganese acetateand ammonium bromide described in Example 24. The yield of terephthalicacid is 101 weight percent.

Example 33 I Manganese acetyl acetonate, one part, is substituted formanganese acetate in Example 24 to yield 102 weight percent ofterephathalic acid.

Example 34 Manganese tl -hydroxy quinolate.(2 parts) is substituted formanganese acetate in Example 24 to yield 105 weight percent ofterephthalic acid.

t 8 Example 35 Two parts. of the manganese complex of ethylene diaminetetracetic acid are substituted for manganese acetate in Example 24 toyield weight percent of terephthalic acid.

Example 36 One part of manganese borate in place of manganese acetate inExample 24 produces weight percent of terephthalic acid.

Example 37 One part of manganese chloride in place of manganese acetatein Example 24 yielded 102 weight percent of terephthalic acid.

Example 38 The use of free bromine, one part, substituted for theammonium bromide in Example 24 yields 116 weight percent of terephthalicacid.

Example 39 Potassium bromate, one part, is substituted for ammoniumbromide in Example 24 and a yield of 124 weight percent of terephthalicacid is obtained.

Example 40 Tetrabromoethane, one part, is substituted for ammoniumbromide in Example 24 and a yield of 126 weight percent of terephthalicacid is obtained.

Example 41 Benzyl bromide, one part, in place of ammonium bromide inExample 24 gives a yield of 103 weight percent of terephthalic acid.

Example 42 Two part of a 50% manganese nitrate solution and 0.75 part ofammonium bromide are charged into the reactor of Example 24 containing75 parts of p-xylene and parts of ace-tic acid. Terephthalic acid isobtained in a weight yield of 108% Example 44 One hundred parts ofcumene, 150 parts of acetic acid, one part of manganese acetate and 0.75part of ammonium bromide are charged to the oxidation reactor of Example24. The oxidation is conducted at 400 p. s. i. g., 3000 volumes/ hour/reaction mixture volume exit gas flow and 400-420 F. for two hours. Theconcentration of carbon dioxide in the outlet gas reaches 6.6% and theoxygen concentration in the vent gas reaches a minimum of 1.0%. Thereactor contents collected are 275.1 parts and form a clear solution.Two hundred and seventyfive parts of water are added to the reactordrainings at room temperature. The solids which precipitate are filteredand washed with 250 parts of water. The precipitate is dried in an ovenat 60 C. and a weight or" 52.4 gramsof-benzoic acid are obtained. Thefiltrate-and water Wash are combined and additional solids precipitated.The second crop of solids is filtered and washed with 100 parts ofwater. A dry weight of 2.4 parts of benzoic acid is obtained. Theprecipitation procedure is repeated three more times by combining eachwater wash with the main filtrate. There were obtained 1.9 parts, 0.6.partand 0.1 part respectivelyot benzoic acid. Thus aitotal of.57.4 partsof benzoic acid is obtained'from 100 grams of cumene feed.

9 Example 45 Onepart of manganese bromide is used in'place of manganeseacetate and ammonium bromide in Example 44. The benzoic acid product isisolated by the same water dilution technique. A total yield of 55.8% ofbenzoic acid is obtained.

Substitution of an equal weight of toluene in the foregoing example forthe :cumene there used gives a weight yield of 117% benzoic acid.

Insimilar manner, with 100 parts ethyl benzene and 150 parts acetic acida 90 percent yield of benzoic acid is obtained (79% of theory); also,p-tertiary-butyl-toluene gives 104 weight percent yield of thecorresponding benzl'oic acid, but no dicarboxylic acid. At 485 F.utilizing caproic acid in place of the acetic acid, a 10% weight yieldof terephthalic acid is obtained from p-tertiary butyltoluene. In amanner similarto Example 21, pentamethylbenzene gives amethylbenzeneatetracarboxylic acid.-

In some cases an induction period of. up to several hours is notedbefore reaction occurs, e. g., when maganese fluoride is used inplace ofmanganese acetate, and in conjunction with ammonium bromide. This isshown in the following example.

Example 46 A reaction mixture of 75 parts para-xylene, 150 parts aceticacid, 1 part manganese fluoride and 0.75 part ammonium bromide is addedto the reactor of Example 24. The reactor charge is maintainedat 410 F.for two hours Without evidence of oxygen absorption. Suddenly thereaction commences and normal oxygen absorption is observed during thenext hour. A yield of 77 grams of terephthalic acid (103% weight yield)is obtained following the standard workup of the reaction mixture asdescribed in Example 1.

Initiators such as peroxides, aldehydes, ketones and the like may beutilized to minimize the length of the induction period.

Example 47 Seventy-five parts of triethylbeneze are oxidized accordingto the procedure of Example 24 for three hours at 400-420 F. in thepresence of 150 parts acetic acid, 1

part managanese acetate and 0.75 part of ammonium bromide. The reactorcontents are drained and filtered. The filter cake is slurried with 50parts of acetic acid (wash) and filtered. The dry weight of tribasicacid obtained is 28.7 grams, which corresponds to a weight yield of 38%.

Example 48 The ammonium bromide is omitted from the reactor chargedescribed in Example 47. Only 1 part of tribasic acid was obtained,which corresponds to a weight yield of 1.3%.

Example 49 i 3 action.

It has been found the reaction medium may be cyclohexane carboxylic acidin place of acetic acid for the oxidation of paradiisopropylbenzene toterephthalic acid.

To the reactor of Example 24 there are charged 125 partspara-di-isopropylbenzene 125 parts cyclohexane carboxylic acid 2 partsmanganese bromide.

The oxidation is carried out for 4 hours at 400-420 F. There is obtained29.3 parts terephthalic acid which mam Y l0 mediate oxidation productsof the materialbeing oxidized, can: be used to advantage.

For example, in a single cycle run. of the type of Example 1, exceptwith no acetic acid medium. a. low yield of terephthalic acidfisobtained (about 8 to 20% by weight) together with a large amount oftoluic acid. By recovering .the former and recycling the latterv acidwith fresh. hydrocarbon feed, and operating at temperatures above themelting point of toluic acid, substantial.- ly complete conversion ofthe hydrocarbon feed to terephthalic acid may be obtained.

In general, according to the present invention it .is possible to obtainyields of carboxylic acids" in excess of 50% by weight per pass thusreducing the amount of recycle necessary toobtain high ultimate oroverall yields and in many instances obviating the necessity ofrecycling.

The process of the present invention can-be conducted on a continuous,intermittent or batch basis. Water may be removed to maintain desiredconcentration, e. g., by distillation, by adding acetic anhydride, orthe like;

Among further metals which can beutilized conjointly with bromine tooxidize an aliphatic substituted aromatic compound to a correspondingcarboxy aroe Desirable orcomparable results may be achieved with variousmodifications of the foregoing within. the broad range set forth herein,thus: the pressure should be sufficient to maintain a liquid phasewhich, if a solvent is used should contain at least some of the saidsolvent. Generally, the pressure may be in the range of atmospheric upto about 1500 p. s. i. g.

The substituted aromatic material fed into the reactor may be analkylbenzene (one to six methyl and the like alkyls), in technicallypure form, free from contaminants or materials which may interfere withthe oxidation re It maybe a mixture of isomeric materials or such amixture containing lower or higher homologues. It may also contain somesaturated aliphatic hydrocarbon materials of similar boiling ranges.Mixtures of materials may be used, converted to the correspondingmixtures of aromatic carboxylic acids, which acids may then beseparated, e. g., by physical means such as distillation, or by acombination of chemical and physical means such as esterificationfollowed by fractionation.

In one aspect of the invention, a polymeric hydro-' carbon. materialused may be prepared in a manner analogous to the preparation of thehydrocarbon of Ex ample-23 except reacting benzene With ethylene'dichloride; Such polymeric materials are known and contain a higher'multiplethan ditolylethane of the following units wherein the end positions ofthe chain may be occupied by a hydrogen atom or a phenyl group; and n isan integer, of about 2 to 12, or up to 20 or more. An importantadvantageof this type of compound is that dibasic acids may be preparedtherefrom.

Instead of using ethylene dichloride to prepare the above polymericmaterial, other analogous aliphatic dichloride may be used, eachchlorine being on different carbon atoms, which carbon atoms may bedirectly joined or may be separated by one or more carbon atoms up toabout 6. However, for economic reasons, ethylene dichloride ispreferred.

Aliphatic substituents on the aromatic nucleus may be bifunctionalgroups attached to two different aromatic carbon atoms, e. g., phthalideor tetrahydronaphthalene which latter compound provides two aliphaticcarbon atoms for each substituted aromatic carbon atom. This is withinthe range of 1 to 4 aliphatic carbon atoms per substituted aromaticcarbon atom as discussed above. All or part of the aromatic carbon atomsmay be substituted by an aliphatic group and two or more of thesubstitutents may be converted to the corresponding carboxylic acidgroup.

Partial oxidation products of the above-mentioned materials may also betreated according to the present invention, e. g., alkaryls or the likewherein the aliphatic substituents are converted to intermediateoxygenated derivatives such as alcohols, aldehycles, ketones, peroxidetype compounds, and the like.

The substituted aromatic compounds which are treated in accordance withthe invention may contain one aromatic nucleus or may be polynnclear; e.g., benzene, naphthalene, anthracene, phenanthreue, dliphenyl,triphenyl, and the like, having the above-mentioned aliphaticsubstituents. These include methylbenzene, ethylbenzene, npropylbenzene,i-propylbenzene, n-butylbenzene, s-butylbenzene, cyclohexylbenzene,dimethylbenzene, diethylbenzene, di-n-propylbenzene, di-i-propylbenzene,di-nbutylbenzene, di-s-butylbenzene, trimethylbenzene, triethylbenzene,tri-n-propylbenzene, tri-i-propylbenzene, trin-butylbenzene,tri-s-butylbenzene, ethyltoluene, ethyl-npropyltoluene,ethyl-i-propyltoluene, ethyl-s-butyltoluene, diethyltoluene,diethyl-n-propyltoluene, diethyl-i-propyltoluene,diethyl-s-butyltoluene, triethyltoluene, triethyl-npropyltoluene,triethyl-i-propyitoluene, triethyl-s-butyltol uene,n-propylethylbenzene, i-propyleth lbenzene, n-butylethylbenzene,s-butylethylbenzene, dimethylethylbenzene, di-n-propylethylbenzene,di-i-propylethylbenzene, di-nbutylethylbenzene, di-s-butylethylbenzene,trimethylethylbenzene, tetraethylbenzene, tri-n-propylethylbenzene,trii-propylethylbenzene, tri-n-butylethyloenzene,tri-s-butylethylbenzene, i-propyl-n-propylbenzene,n-butyl-n-propylbenzene, s-butyl-n-propylbenzene,dimethyl-n-propylbenzene, di-i-propyl-n-propylbenzene,di-n-butyl-n-propylbenzene, di-s-butyl-n-propylbenzene,trimethyl-n-propylbenzene, triethyl-n-propylbenzene,tri-n-propylbenzene, tri-i propylbenzene, tri-n-butyl-n-propylbenzene,tri-s-butyl-npropylbenzene, n-butyl-i-propylbenzene,s-butyl-i-propylbenzene, dimethyl-i-propylbenzene,diethyl-i-propylbenzene, di-i-propylbenzene,di-n-propyl-i-propylbenzene, dis-butyl-i-propylbenzene,trimethyl-i-propylbenzene, triethyl-i-propylbenzene,tri-i-propylbenzene, tri-n-butyl-ipropylbenzene, i-butyLn-butylbenzene,dimethyl-i-butylbenzene, diethyl-i-butylbenzene,di-n-propyl-i-butylbenzene, di-i-propyl-i-butylbenzene,di-n-butyl-i-bntylbenzene, di-s-butyl-i-butylbenzene,trimethyl-i-butylbenzene, triethyl i butylbenzene, tri n propyl ibutylbenzene, tri-i-propyl-i-butylbenzene, dimethyl-s-butylbenzene, diethyl s butylbenzene, di n propyl s butylbenzene,di-i-propyl-s-butylbenzene, di-n-butyl-s-butylbenzene, trimethyl sbutyl'oenzene, triethyl s butylbenzene, trin-propyl-s-butylbenzene,tri-i-propyl-s-butylbenzene, tri-nbutyl-s-butylbenzene, andcorrespondingly (or higher) substituted polynuclear materials; alsoalpha-methyl naphthalene, beta-methyl naphthalene, dimethyl biphenyl,methyl acetophenones, toluic acids, acetobenzoic acids and1,3-dimethyl-4-chloro-benzene (the isophthalic acid derivative resultingfrom the latter may be converted to This application is acontinuation-in-part of the copencling applications Serial No. 427,370,filed May 3, 1954; Serial No. 427,865, filed May 5, 1954;Serial No.431,588, filed May 21, 1954; Serial No. 495,347, filed May 18, 1955;Serial No. 435,915, filed June 10, 1954; and Serial No. 435,916, filedJune 10,1954, all of which are now abandoned.

in view of the foregoing disclosures, variations and modifications ofthe invention will be apparent to those skilled in the art, and it isintended to include within the invention all such variations andmodifications except as do not come within the scope of the appendedclaims.

We claim:

1. A process for producing a polycarboxylic aromatic acid whichcomprises reacting in a reaction zone, while, maintaining a liquid phasein said zone, an aromatic compound selected from the group consisting ofpolyalkyl aromatic compounds and intermediate oxygenated derivativesthereof with molecular oxygen in the presence of a catalyst comprisingin conjoint presence bromine and a heavy metal oxidation catalyst andrecovering said polycarboxylic aromatic acid.

2. A process as defined in claim 1 wherein the metal is in ionic form.

3. A process as defined in claim 1 wherein the bromine is in ionic form.

4. A process as defined in claim 1 wherein the heavy metal has an atomicnumber of 23 to 28 inclusive.

5. A process defined in claim 1 wherein the heavy metal is cerium.

6. A process as defined in claim 1 wherein the heavy metal is manganese.

7. A process as defined in claim 1 wherein the heavy metal comprisesmanganese and cobalt.

8. A process as defined in claim 1 carried out in the presence of amonocarboxylic acid having 1 to 8 carbon atoms in the molecule.

9. A process as defined in claim 8 wherein the mono carboxylic acid isacetic acid, the temperature is in the range of to 275 C. and thepressure is in the range of 0 to 1500 p. s. i. g.

10. A process for producing a polycarboxylic aromatic acid whichcomprises reacting in a reaction zone, while maintaining a liquid phasein said zone, a xylene with molecular oxygen in the presence of acatalyst comprising in conjoint presence bromine and a heavy metal oxidation catalyst and recovering said polycarboxylic aromatic acid.

11. A process for producing a polycarboxylic aromatic acid which is amember of the group consisting of alkyl substituted dicarboxylicaromatic acid, tricarboxylic aromatic acid and mixtures thereof whichcomprises reacting in a reaction zone, while maintaining a liquid phasein said zone, a trialkyl benzene, in which the alkyl substituentscontain 1 to 4 atoms of carbon, with molecular oxygen in the presence ofa catalyst comprising in conjoint presence bromine and a heavy metaloxidation catalyst and recovering said carboxylic aromatic acid.

12. A process as defined in claim 11 wherein the trialkyl benzene is atrimethyl benzene.

References Cited in the file of this patent UNITED STATES PATENTS2,245,528 Loder et al. June 10, 1941 2,276,774 Henke et al Mar. 17, 19422,723,994 Haefele et al Nov. 15, 1955 FOREIGN PATENTS 1,017,881 FranceOct. 1, 1952

1. A PROCESS FOR PRODUCING A POLYCARBOXYLIC AROMATIC ACID WHICHCOMPRISES REACTING IN A REACTION ZONE, WHILE MAINTAINING A LIQUID PHASEIN SAID ZONE, AN AROMATIC COMPOUND SELECTED FROM THE GROUP CONSISTING OFPOLYALKYL AROMATIC COMPOUNDS AND INTERMEDIATE OXYGENATED DERIVATIVESTHEREOF WITH MOLECULAR OXYGEN IN THE PRESENCE OF A CATALYST COMPRISINGIN CONJOINT PRESENCE BROMINE AND A HEAVY METAL OXIDATION CATALYST ANDRECOVERING SAID POLYCARBOXYLIC AROMATIC ACID.